Hawksbill turtles’ monogamous sex life revealed

The sex lives of critically endangered hawksbill turtles have been revealed by scientists studying the animals in the Seychelles.

Previously, little had been understood about the mating habits of the turtles, which live underwater and often far out at sea.

Researchers were surprised to find that the turtles are mainly monogamous, with females storing sperm from one male and using it to fertilise multiple egg clutches.

The study, led by researchers from the University of East Anglia, Norwich, UK, was published in the online journal Molecular Ecology.

“Sperm storage” is found in animals including reptiles, birds and some turtles, tortoises and terrapins.

Females can store viable sperm from multiple males for long periods of time, meaning that their egg clutches are sometimes fertilised by more than one father.

Researchers carried out DNA testing from hawksbill turtle hatchlings on Cousine Island in the Seychelles to identify how many males were involved in fertilising eggs during a breeding season.

The tests revealed a monogamous mating system: most egg clutches were sired by just one male, and no males had fertilised more than one female during the 75-day season.

“We were surprised that they were so monogamous because actually… genetic monogamy is actually the exception in most animals, not the rule,” said research team member Dr David Richardson.

The findings show that “there are plenty of males out there” for females to mate with.

“It’s very unlikely that it’s just a few males hanging around offshore”, said Dr Richardson. “We think they’re mating with males a long way away, wherever they’re normally foraging and feeding which can be all over the western Indian Ocean,” he added.

The number of hawksbill turtle males contributing to the next generation is important for the species’ survival because it results in higher levels of genetic variation.

Genetic variability “means [the turtles] can respond to new threats, new diseases or anything that comes along,” explained Dr Richardson.

Hatchling turtles return to the sea

Hawksbill turtles were identified as Critically Endangered by the International Union for the Conservation of Nature after years of being hunted for their shells, which were prized in the now illegal decorative tortoiseshell trade.

Found in tropical waters around the world, females turtles gather at onshore nesting sites such as Cousine Island every few years to lay around five clutches of eggs during the season.

Mating often takes place out at sea, but according to the study, by testing DNA samples from hatchlings on the island, the researchers were able to gather information that would have been impossible from observation alone.

Dr Richardson told BBC Nature that this study, combined with independent reports of hawksbill turtle numbers rising, indicates that “in terms of conservation… maybe we are in a better place than we thought.”

The team hopes their study may help conservationists working on Cousine Island to understand more about the lives of the animals and to focus their efforts.